Predominantly, exercise apparatuses that utilize selectorized weight stacks as a source of resistance, also incorporate some type of range-limiting device. These devices usually allow a user to select a desired starting point and stopping point along a particular range of motion (ROM). Furthermore, they play a significant role in medical rehabilitation programs where ROM variables such as a users' injury, flexibility, size or desired exercise must be accommodated.
Generally, range-limiting devices operate in-line to selectorized weight stacks and require an additional step in machine set-up. These devices are often times elaborate, unreliable and expensive. U.S. Pat. No. 4,603,855 discloses a variable exercise apparatus incorporating a range-limiting device that provides selective positioning of a cable attached handle along a ROM. This device takes-up and pays-out cable from a drum to the attached handle and is selectively engageable by a clutching means to an additional drum and cable system that operates the selectorized weight stack. To operate, a user first engages a selected resistance level and then engages the clutching device at a selected handle position.
Many strength system manufacturers produce range-limiting devices that operate in-line to their selectorized weight stacks. These devices provide selective start and stop positioning of those user engageable elements or ROM elements adapted to transmit a lifting force to an in-line selectorized weight stack. To operate, a user or physical therapist must first select a desired resistance level and then make a ROM selection. ROM selection includes a starting and stopping point selection. Starting point selection is achieved via a free wheeling ROM element acting about an axle attached cam that is selectively engageable at 10 degree increments to the axle by an engaging pin means; and a stopping point selection, via an axle stop device that is selectively engageable at 10 degree increments by an additional engaging pin means, and prevents further axle rotation. Therefore, a ROM selection involves a cumbersome task of releasing and engaging a pair of engaging pins while positioning ROM elements to a desired starting position. Another inherent drawback to this type of range-limiting device, involves a cam that disengages with a ROM selection, resulting in an incorrect biomechanical variable resistance throughout a selected ROM.